Long-term changes of plumage between urban and rural populations of white-crowned sparrows (Zonotrichia leucophrys)

Abstract

Urbanization is one of the most extreme forms of land transformation and results in changes to ecosystems and species compositions. As a result, there are strong directional selection pressures compared to nearby rural areas. Despite a surge in research on the different selection pressures on acoustic communication in urban and rural areas, there has been comparatively little investigation into traits involved with visual communication. We measured the plumage of museum specimens of white-crowned sparrows (Zonotrichia leucophrys) from urban and adjacent rural habitats in San Francisco, CA, to assess the effects of divergent habitats on plumage. We found significant differences in dorsal plumage, but not crown plumage, between urban and rural populations that have been diverging over the past 100 years. Urban birds have increasingly darker and duller dorsal plumage, whereas rural birds in adjacent areas have plumage with richer hues and more color complexity. Our findings suggest a newly observed adaptation to urban environments by native species and suggest that many traits, in addition to acoustic signals, may be changing in response to urban selection pressures. Additional collections in urban areas are needed to explore likely divergences in plumage coloration between urban and rural environments.

Phenotypic signatures of urbanization? Resident, but not migratory, songbird eye size varies with urban‐associated light pollution levels

“…Differences in age structure between urban and more natural habitats remains a largely overlooked factor that can mediate associations between urbanization and phenotypic traits of interest (Kozlovsky et al, 2021). While some studies have documented clear differences in phenotypic traits between urban and rural habitats (e.g., Liker et al, 2008; Meillere et al, 2015; Smith et al, 2021), few studies have explicitly tested for the confounding effects of age on avian responses to urbanization. And as our findings with the buntings clearly demonstrate, failure to explicitly test for relationships between urbanization, age, and age structures makes it difficult to fully address potential drivers of phenotypic variation in the face of urbanization (Kozlovsky et al, 2021), and as a consequence, may produce misleading results.…”

“…Differences in age structure between urban and more natural habitats remains a largely overlooked factor that can mediate associations between urbanization and phenotypic traits of interest (Kozlovsky et al, 2021). While some studies have documented clear differences in phenotypic traits between urban and rural habitats (e.g., Liker et al, 2008;Meillere et al, 2015;Smith et al, 2021), few studies have explicitly tested for the confounding effects of age on avian responses to urbanization.…”

“…In birds, research in urban ecology has revealed many cases of phenotypic divergence between conspecifics in urban and more natural habitats, including but not limited to a range of morphological, physiological, and behavioral traits (e.g., Corsini et al, 2022; Jones et al, 2010; Liker et al, 2008; Smith et al, 2021). One trait of particular interest to ecologists has been body size.…”